1. Technical Field
The present invention relates to a high-voltage driver, and a piezoelectric pump unit incorporating a piezoelectric pump and its control board in the same housing.
2. Related Art
A piezoelectric pump has a variable volume chamber (liquid pump chamber) formed between a flat piezoelectric vibrator and a housing, and causes the piezoelectric vibrator to vibrate to thereby change the volume of the variable volume chamber and achieve the pumping action. More specifically, in a pair of paths connected to the variable volume chamber, a pair of check valves for different flow directions (a check valve which allows fluid flow into the variable volume chamber and a check valve which allows fluid flow from the variable volume chamber) are provided, respectively, and, when the volume of the volume variable chamber is changed by the vibration of the piezoelectric vibrator, the operation of opening one of the pair of check valves and closing the other is repeated, thereby achieving the pumping action. Because such a piezoelectric pump is used as a cooling water circulating pump for, for example, a water-cooled notebook computer, reducing the size and the thickness of the pump becomes a key issue.
[Patent Document 1] JP 6-109068 A
[Patent Document 2] JP 8-205563 A
[Patent Document 3] JP 2000-60847 A
In order to reduce the size of the piezoelectric pump, it is advantageous to contain the piezoelectric vibrator and a control board (driver) feeding this piezoelectric vibrator with a drive signal in the same housing. Further, as the control board of the piezoelectric pump generates high voltage, in terms of obtaining UL (Underwriters Laboratories Inc.) approval as well, it is essential to contain the control board in the housing. However, with a conventional control board, drive control parts for a piezoelectric vibrator, such as a waveform generating circuit generating a sinusoidal signal for drive control use, a booster circuit boosting an input signal from a power supply, and a high-voltage control circuit feeding the piezoelectric vibrator with a high-voltage drive signal obtained by synthesizing the boosted voltage signal and the sinusoidal signal, are composed of analog circuits. Therefore, the circuit scale is too large to be contained in the housing. JP 8-205563 A discloses the use of a transmitter composed of such analog circuits, as a reference pulse transmitter. In contrast to this, when the drive control parts on the control board are composed of digital circuits, although their smaller circuit scale enables a smaller and thinner control board, a sinusoidal signal for drive control use is generated by a digital waveform, and therefore, a steep voltage change occurs locally, resulting in a non ideal sinusoidal wave (see FIG. 8C). When a high-voltage drive signal obtained by synthesizing this non smooth sinusoidal digital signal and the boosted voltage signal is fed to the piezoelectric vibrator, the piezoelectric vibrator responds to the steep voltage change of the high-voltage drive signal, resulting in noise generation. Although, in order to remove the steep voltage change of the sinusoidal digital signal, it is possible to enhance the resolution of the time axis and the voltage axis when generating the sinusoidal digital signal, this is not realistic because the circuit scale becomes enormous in order to achieve such resolution. Further, although JP 6-109068 A and JP 2000-60847 A disclose configurations that use a digital/analog converter to generate signals for a piezoelectric actuator and a piezoelectric ceramic plate simply in order to cancel vibration of an engine of an automobile and external environmental noise, such configurations are used merely to cancel vibration and noise in large-size apparatuses like an automobile and a bioacoustic detecting apparatus, and these patent documents fail to recognize the problems to be overcome when a small-size electronic device is to be used by integrating into a piezoelectric pump that constantly causes a diaphragm to vibrate.